The present invention relates to a method for manufacturing electrical components of the energy-accumulating electrostatic or electrochemical type (such as for example plastic film capacitors, double-layer capacitors, supercapacitors and primary and secondary batteries), to the machine that performs the method, and to the components provided according to the method (for example with said machine).
The current method of providing film-type capacitors made of a metallized material such as plastics (hereinafter termed simply “metallized plastic film”, that is assumed to include all of the films made of polymeric materials or with natural rubbers having at least one surface coated with an electrically conducting material) entails a first winding step, during which two or more superimposed plastic films are wound onto a support (having variable shapes and dimensions depending on the geometric and electrical characteristics of the capacitor to be provided). Mechanical compaction is then performed by applying pressure (associated with heating or not) in order to give the component a structural consistency and stability that are substantially constant over time.
A layer of conducting material is then applied (usually by spraying) on the plastic films to provide an interface between the metalized layer that is already present on one surface of the wound plastic films (with a thickness in the region of 400 angstroms) and the electrical terminations for the flow of current. The metallic terminals (designed to feed the current) that will allow to connect the capacitor to an electric circuit are in fact soldered to these deposited metallic interfaces. As a final step, the capacitor is inserted in the corresponding casing and sealed therein by pouring particular thermosetting resins.
The advantage of this type of production arises from various factors: first of all, the high stability of the electrical characteristics over time, the capability to work with high transient or continuous voltages thanks to the self-regeneration of the material used as dielectric, the possibility to work at high frequencies thanks to the low dielectric losses, the possibility to bear high current peaks, and a failure behavior similar to that of an open circuit (open-type failure mode).
By following this constructive principle, substantially two different types of capacitor are currently manufactured: wound capacitors and stacked layer capacitors.
In wound capacitors, two or more plastic films having at least one metallized surface are wound onto a support (that can be made of substantially any material), which can be removed or not at the end of the winding process. If said support is left inside the capacitor, the shape of the capacitor will be substantially cylindrical; if the support is removed, as a consequence of compaction the capacitor will generally assume a substantially oval shape. Thermomechanical stabilization, deposition of the metallic layer to which the terminals for feeding current will be connected, and impregnation in a resin lead to the finished product.
The resulting component has limited flexibility in occupying the various geometric requirements of the end user (particularly in the case of production of cylindrical components) and in saturating the volume available for installation of the component (the available spaces are generally polygonal and almost never circular).
In stacked capacitors, two or more layers of metallized film are wound on a support that is shaped like a parallelepiped. The final shape of the component is substantially always ovoid but more elongated, depending on the dimensional ratio of the supporting parallelepiped (in practice, the shape duplicates the shape of the initial bar, with ends that are radiused along circular arcs). These wound films are stabilized by compression and then the metallic layer is deposited onto the two surfaces. The radiused ends of the wound films are then removed and the films are divided (by means of a transverse cut) in a plurality of segments having the chosen length (a particular value of capacitance being associated with the length of the component). The critical points of this technology are first of all the high process waste due to the need to eliminate the entire radiused end region (the percentage of waste material can reach as much as 30%); secondly, it must be noted that with this technology it is possible to obtain only elements that have a thickness of no more than 20 mm, since if the thickness is increased it is not possible to maintain the mechanical tolerances related to the coupling between the various layers, which are required in order to ensure stable electrical characteristics. Finally, it should be noted that the region at which cutting occurs is a highly critical point for voltage transients, and due to the difficulty in providing very thick elements, the inductance of capacitors with a high capacitive value is always very high (inductance is directly proportional to the width of the capacitor).